Water treatment glossary
Short definitions of the terms you may see in a water test report or filter quote. Choose a term to jump to its meaning and original source.
- Activated carbon
Carbon with many tiny pores that hold some dissolved substances on its surface. It is used for some taste and smell problems; what it removes depends on the carbon and the water.
Source: US EPA: Overview of Drinking Water Treatment Technologies
Back to the term index- Backwash
Cleaning a filter bed by reversing the water flow to loosen trapped particles and carry them out. The required flow and cleaning cycle depend on the filter and its media.
Source: US EPA: Development Document for the Centralized Waste Treatment Point Source Category (2000)
Back to the term index- Birm
A named filter medium that helps dissolved oxygen turn dissolved iron into particles that can be filtered out. Its use depends on the water chemistry, including pH and oxygen.
Source: Clack Corporation: Birm media technical description
Back to the term index- Chlorides
Dissolved chloride ions, found in salts such as sodium chloride. High chloride levels can give water a salty taste. Chloride is different from chlorine used for disinfection.
Source: USGS: National Water Summary 1990–91, Water-Supply Paper 2400 (Smith, Alexander and Lanfear, 1994); US EPA: Secondary Drinking Water Standards: Guidance for Nuisance Chemicals
Back to the term index- Hardness
The amount of dissolved calcium and magnesium in water. Hard water can leave scale when heated and makes soap less effective.
Source: USGS Water Science School: Hardness of Water
Back to the term index- Iron
A metal that can be dissolved in groundwater or present as particles. It can cause rusty stains and affect water colour or taste. Its form matters when choosing treatment.
Source: Clack Corporation: Birm media technical description; US EPA: Secondary Drinking Water Standards: Guidance for Nuisance Chemicals
Back to the term index- Manganese
A metal that may be present in water and can cause dark stains. Treatment depends on its form and the water chemistry.
Source: US EPA: Secondary Drinking Water Standards: Guidance for Nuisance Chemicals; Clack Corporation: Birm media technical description
Back to the term index- MnO2 (manganese dioxide)
A manganese compound used in some filter media to help turn dissolved metals into particles that can be filtered out. Different media have different operating needs.
Source: Clack Corporation: Filter-Ox media technical description
Back to the term index- Multimedia filter
A filter with layers of different granular materials that trap suspended particles as water passes through. The layers are chosen for the job the filter needs to do.
Source: US EPA: Development Document for the Centralized Waste Treatment Point Source Category (2000)
Back to the term index- pH
A measure of how acidic or alkaline water is. It affects water chemistry and how some treatment media work.
Source: USGS Water Science School: pH and Water; Clack Corporation: Birm media technical description
Back to the term index- RO (reverse osmosis)
A process that pushes water through a membrane under pressure to separate it from many dissolved salts and other substances. It also produces a reject-water stream.
Source: US EPA: Overview of Drinking Water Treatment Technologies
Back to the term index- Settling
Letting suspended particles sink under gravity so the clearer water can move on to the next treatment step. It removes particles that can settle, rather than dissolved salts.
Source: US EPA: Drinking Water Treatment Plant Residuals Management — Technical Report (2011); USGS: National Water Summary 1990–91, Water-Supply Paper 2400 (Smith, Alexander and Lanfear, 1994)
Back to the term index- TDS (total dissolved solids)
The total amount of substances dissolved in water, including salts and minerals. A TDS reading does not identify each substance or tell you whether germs are present.
Source: USGS: National Water Summary 1990–91, Water-Supply Paper 2400 (Smith, Alexander and Lanfear, 1994); CDC: About Home Water Treatment Systems (2024)
Back to the term index- Turbidity
A measure of how much material in water scatters light, often seen as cloudiness. It describes clarity; clear-looking water still needs the right tests for its intended use.
Source: USGS Water Science School: Turbidity and Water
Back to the term index- UF (ultrafiltration)
Filtration through a fine membrane that removes particles and many germs. It does not remove dissolved salts; check the specific filter for what it can remove.
Source: CDC: About Home Water Treatment Systems (2024)
Back to the term index- UV (ultraviolet treatment)
Using ultraviolet light to disinfect water or reduce germs. UV does not remove dissolved chemicals, and filtering the water before UV helps it work.
Source: CDC: About Home Water Treatment Systems (2024)
Back to the term index- Vessel filter
A filter whose treatment media sit inside a vessel through which water flows. The vessel holds the media; the media and design determine what the filter treats.
Source: US EPA: Overview of Drinking Water Treatment Technologies; Clack Corporation: Birm media technical description
Back to the term index- Water softener
A system that removes hardness minerals, mainly calcium and magnesium. A common type uses ion-exchange resin; a softener does not disinfect water.
Source: US EPA: Overview of Drinking Water Treatment Technologies; CDC: About Home Water Treatment Systems (2024)
Back to the term index
Match treatment to your water
These definitions explain the words. They do not replace a water test or the instructions for your installed system.